Acrylic resin composition

ABSTRACT

An acrylic resin is provided which has excellent weatherability, outstanding transparency and improved heat and solvent resistance, as well as improved impact strength. The acrylic resin comprises an intimate blend of a polymerization syrup and a catalytic amount of a polymerization catalyst capable of effecting polymerization of the syrup. The polymerization syrup, which has an improved shelf life and can be stored at ambient temperature and atmospheric pressure, consists essentially of: 
     (a) from about 300 to about 1000 parts per volume of an acrylic monomer represented by the formula ##STR1##  wherein R is an alkyl moiety containing 1 to about 18 carbon atoms; (b) from about 0.1 to about 1 parts by volume of 2,2-bis(allyl-oxymethyl)-butan-1-ol; 
     (c) from about 0.5 to about 5 parts by volume of a mercaptan; and 
     (d) from about 0.3 to about 40 parts by volume of a crosslinking agent compatible with the acrylic monomer. 
     The polymerization syrup can further contain from about 1 to about 100 parts by volume of a polycarbonate compound.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to acrylic resin compositions, and moreparticularly but not by way of limitation, to an acrylic monomer basedpolymerization syrup having an improved shelf life which. In one aspectthe present invention relates to an acrylic monomer containingpolymerization syrup which, upon addition of a quaternary ammonium saltpolymerization catalyst, is curable at ambient temperatures andpressure.

2. Brief Description of the Prior Art

Acrylic resins formed predominantly of methyl methacrylate haveheretofore been known. Because acrylic resins formed of methylmethacrylate are linear polymers, the polymers have exhibited goodweatherability and transparency. However, such polymers have sufferedfrom disadvantages in that they are deficient in resistance to heat,solvents, shock, and surface hardness. Because of these deficiencies theprior art is replete with acrylic based resin compositions wherein thebase polymer, i.e. methyl methacrylate, is copolymerized with otherpolymers in an effort to overcome the before-stated deficiencies of suchresins. Examples of several plastic resin compositions, and methods forproducing such compositions which have heretofore been employed toovercome the inherent deficiencies of the acrylic resin compositionswherein methyl methacrylate is employed as the base monomer are U.S.Pat. No. 4,791,184, issued Dec. 13, 1988 to Nagai, et. al.; U.S. Pat.No. 4,319,003, issued Mar. 9, 1982 to Gardlund; U.S. Pat. No. 4,214,064,issued July 22, 1980 to Kanazawa; U.S. Pat. No. 4,152,506, issued May 1,1979 to Novak; and U.S. Pat. No. 3,957,921, issued May 18, 1976 toIwahashi, et. al.

While various methods and resin compositions have been proposed forimproving the resistance to heat, solvents, shock and surface hardnessof acrylic based resins (without sacrificing the desired properties ofweatherability and transparency of such resins), the resulting modifiedpolymers have a tendency to become colored on heating and the desiredproperties of weatherability, transparency and color are oftensacrificed or reduced.

Thus, it would be desirable if one could develop a polymerization syrupof an acrylic monomer which would maintain all of the desired propertiesof an acrylic resin, while at the same time overcome the knowndeficiencies of an acrylic resin. Further, it would also be desirable ifone could formulate an acrylic resin composition which maintains itsdesired properties when cast into thick sheets or articles, and whichwould be substantially void or bubble free, and which did not requirepost curing. It is to such a polymerization syrup and resin compositionthat the present invention is directed.

SUMMARY OF THE INVENTION

In accordance with the present invention an acrylic resin is providedwhich has excellent weatherability, outstanding transparency andimproved heat and solvent resistance, as well as improved impactstrength. The acrylic resin comprises an intimate blend of apolymerization syrup and a catalytic amount of a polymerization catalystcapable of effecting polymerization of the syrup. The polymerizationsyrup consists essentially of:

(a) from about 300 to about 1000 parts per volume of an acrylic monomerrepresented by the formula ##STR2## wherein R is an alkyl moietycontaining 1 to about 18 carbon atoms;

(b) from about 0.1 to about 1 parts by volume of a non-peroxide oxygendonator, i.e. 2,2-bis(allyl-oxymethyl)-butan-1-ol;

(c) from about 0.5 to about 5 parts by volume of a mercaptan; and

(d) from about 0.3 to about 40 parts by volume of a crosslinking agentcompatible with the acrylic monomer.

The acrylic monomer containing polymerization syrup described above, inaddition to having an improved shelf life, can also be stored at ambienttemperatures and pressure without deterioration of the syrup. That is,the polymerization syrup of the present invention can be stored andtransported without the need of refrigeration. However, the shelf lifeof the polymerization syrup has been enhanced by the addition of fromabout 1 to about 100 parts by volume of a polycarbonate compound such asallyl diglycol carbonate.

An object of the present invention is to provide a novel acrylic resinand a method for the production thereof.

Another object of the present invention, while achieving the beforestated object, is to provide an acrylic resin excelling in physicalproperties, such as heat and solvent resistance without sacrificing thedesired properties of transparency and weatherability.

Yet another object of the present invention, while achieving the beforestated objects, is to provide a polymerization syrup for an acrylicresin which, when admixed with an effective amount of a polymerizationcatalyst, permits the resulting resin composition to be cured at ambienttemperatures and pressure.

Still another object of the present invention, while achieving thebefore stated objects, is to provide a polymerization syrup for anacrylic resin having improved shelf life.

Other objects, advantages and features of the present invention willbecome apparent upon reading of the following detailed description inconjunction with the appended claims.

DETAILED DESCRIPTION

The present invention provides a polymerization syrup having an improvedshelf life which, when admixed with a catalytic amount of apolymerization catalyst capable of effecting polymerization of thesyrup, provides an acrylic resin composition which is curable at ambienttemperatures and pressure. The polymerization syrup consists essentiallyof:

(a) from about 300 to about 1000 parts by volume of an acrylic monomerrepresented by the formula ##STR3## wherein R is an alkyl moietycontaining 1 to about 18 carbon atoms;

(b) from about 0.1 to about 1 parts by volume of a non-peroxide oxygendonator, such as 2,2-bis(allyloxymethyl)-butan-1-ol;

(c) from about 0.5 to about 5 parts by volume of a mercaptan; and

(d) from about 0.3 to about 40 parts by volume of a crosslinking agentcompatible with the acrylic monomer.

In formulating the polymerization syrup of the present invention, anysuitable acrylic monomer represented by the formula ##STR4## wherein Ris an alkyl moiety containing 1 to about 18 carbon atoms, more desirablyfrom 1 to 8 carbon atoms can be employed provided that the acrylicmonomer is a liquid at ambient temperature. Examples of alkyl moietiessatisfying the definition for R of the beforedescribed formula includemethyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl,decyl, undecyl, dodecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl,octadecyl and the like. Specific examples of an acrylic monomersatisfying the above defined formula include methyl methacrylate, ethylmethacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate,cyclohexyl methacrylate, ω-hydroxyalkyl methacrylates, and the like.

The mercaptan employed in the formulation of the polymerization syrup isrepresented by the general formula

    RSH

wherein R contains from 1 to about 22 carbon atoms. Further, R can beany suitable moiety, such as an alkyl moiety, a cycloaliphatic moietyand the like. Illustrative of such mercaptans are methyl mercaptan,propyl mercaptan, dilimonen dimercaptan, cyclohexyl dimercaptan,ethylcyclohexyl dimercaptan and mixed primary tridecyl mercaptan.

It should be noted that the only requirement for the mercaptan is thatthe mercaptan be in liquid form under the conditions of mixing, and thatthe mercaptan be compatible with the particular acrylic monomer employedin the formulation of the polymerization syrup, as well as with thenon-peroxide oxygen donator, i.e. 2,2-bis(allyloxymethyl)-butan-1-ol,and the crosslinking agent employed in the formulation.

In order to produce an acrylic resin which can be cured at ambienttemperatures and pressure, that is, without the requirement of a postcuring step, the polymerization syrup (in addition to the acrylicmonomer, the non-peroxide oxygen donator and the mercaptan) furtherincludes a crosslinking agent. The amount of crosslinking agent employedcan vary widely and will be determined to a large degree by theefficiency of the crosslinking agent when admixed with a polymerizationcatalyst. That is, for a strong crosslinking agent such as ethyleneglycol dimethacrylate, the concentration of the crosslinking agentrequired will be slightly more. However, it has generally been foundthat when formulating a polymerization syrup of the present inventionthat the amount of crosslinking agent, although same can vary widely,will generally be from about 0.3 to about 40 parts by volume of thecrosslinking agent. Typical crosslinking agents which may be employed inthe formulation of the polymerization syrup, in addition to ethyleneglycol dimethacrylate, include allyl methacrylate, allyl acrylate,ethylene glycol diacrylate, polyethylene glycol dimethacrylate,diethylene glycol dimethacrylate, and triethylene glycol dimethacrylate.

As previously indicated, the amount of crosslinking agent incorporatedinto the polymerization syrup can vary widely, depending to a largedegree on the particular crosslinking agent employed. However, desirableresults can generally be obtained when the crosslinking agent isincorporated into the syrup in an amount sufficient to provide fromabout 0.3 to about 40 parts by volume of the crosslinking agent.

To stabilize the polymerization syrup and thus enhance the shelf life ofthe syrup, the polymerization syrup may further include an effectiveamount of a polycarbonate compound. The amount of polycarbonate compoundincorporated into the polymerization syrup can vary widely but willgenerally be in an amount to provide from about 1 to about 100 parts byvolume of the polycarbonate compound in the syrup.

Any suitable polycarbonate compound which is compatible with the acrylicmonomer can be employed in the formulation of the polymerization syrup.However, desirable results have been obtained wherein the polycarbonatecompound is allyl diglycol carbonate.

It should be noted that in formulating a polymerization syrup as setforth above, one does not need to incorporate polymerization inhibitorsinto the syrup in order to prevent undesired or prematurepolymerization. That is, it has been unexpectedly found that the shelflife of the polymerization syrup can be improved to a desirable level,without the need of refrigeration, when the syrup is formulated as setforth above; and that the shelf life can be further enhanced byincorporation of from about 1 part to about 100 parts by volume of thepolycarbonate compound per volume of the syrup, and more desirably fromabout 25 to about 50 parts by volume of the polycarbonate compound.

To enhance mold release it is often desirable to incorporate into thepolymerization syrup an effective minor amount of an internal moldrelease agent. The amount of the internal mold release agent can varywidely, but will generally be in an amount sufficient to provide thesyrup with from about 0.01 to about 2 parts per volume of the internalmold release agent.

Any suitable internal mold release agent can be employed in theformulation of the polymerization syrup provided that the mold releaseagent is compatible with the other ingredients constituting the syrup.For example, desirable results have been obtained wherein the internalmold release agent is a surfactant, and wherein the surfactant is ananionic or nonionic surfactant which is compatible with the acrylicmonomer and which does not reduce the transparency of the resultingpolymeric resin. Examples of the suitable anionic surfactant include:

sodium alkyl sulfate, (such as sodium octylsulfate, sodiumlaurylsulfate, sodium stearylsulfate);

sodium alkylbenzenesulfates, such as sodium dodecylbenzenesulfate;

sodium alkylsulfonates, such as sodium cetylsulfonate and sodiumstearylsulfonate;

sodium dialkyl sulfosuccinates, such as sodium dioctyl sulfosuccinate,and the like.

Examples of nonionic surfactants include:

polyethyleneglycol alkyl ethers, such as polyethyleneglycol oleyl ether,polyethyleneglycol lauryl ether, and the like;

polyethyleneglycol alkylphenyl ethers, such as polyethyleneglycolnonylphenyl ether;

higher fatty acid esters of polyethyleneglycol, such as oleic acid esterof polyethyleneglycol, stearic acid ester of polyethyleneglycol, lauricacid ester of polyethyleneglycol, and the like;

polyethyleneglycol polypropyleneglycol ether;

sorbitan fatty acid esters, such as sorbitan monolaurate, sorbitanmonostearate, and the like;

polyethyleneglycol sorbitan fatty acid esters, such aspolyethyleneglycol sorbitan monolauric acid ester, polyethyleneglycolsorbitan monooleic acid ester, phosphoric acid esters ofpolyethyleneglycol; and

phosphoric acid esters of alkylpolyethyleneglycol and the like.

The surfactants listed above are merely illustrative of anionic andnonionic surfactants which can be employed as the internal mold releaseagent in the formulation of the polymerization syrup of the presentinvention. However, desirable results have been obtained wherein thesurfactant is sodium dioctyl sulfosuccinate.

A polymerization syrup formulated as set forth above, whether sameincorporates the polycarbonate compound and/or the mold release agent,can be catalyzed by a catalytic amount of quaternary ammonium saltsgenerally known as "fabric softeners". The acrylic resin formulated fromthe polymerization syrup and the quaternary ammonium salt catalystprovides a resin molding material which can be cured at ambienttemperatures and atmospheric pressure to produce articles having thedesired properties of an acrylic resin, that is, the desired propertiesof transparency and weatherability, while improving the impact strengthand the heat and solvent resistance of the resin composition. Further,it should be noted that when employing the resin composition, articlescan be molded having a thickness of up to four inches or greater whichdo not require post curing treatment, and are substantially void orbubble free. Thus, it becomes apparent that the unique polymerizationsyrup and the resin which results from admixing a catalytic amount ofthe quaternary ammonium salt polymerization catalyst with the syruprepresents an advance in the state of the art of acrylic resins.

As previously stated, the quaternary ammonium salt employed as thecatalyst for the polymerization syrup of the present invention aregenerally known in the industry as "fabric softeners". Illustrativeexamples of such quaternary ammonium salts are as follows:

Dialkyldimethylammonium chlorides, such as dicocodimethylammoniumchloride and ditallowdimethylammonium chloride;

Dialkyldimethylammonium methylsulfates;

Alkyltrimethylammonium chlorides, such as soya trimethylammoniumchloride, hydrogenated tallow trimethylammonium chloride,palmityltrimethylammonium chloride, cocotrimethylammonium chloride,tallow trimethylammonium chloride, and benzyltrimethylammonium chloride;and

Alkyldimethylbenzylammonium chlorides, such as dimethylalkyl (C₁₄ -C₁₈)benzylammonium chloride and dimethylalkyl (C₁₂ -C₁₆) benzylammoniumchloride.

It should be noted that the above examples are merely illustrative ofthe quaternary ammonium salts which can be used in the formulation ofthe additive for polyester resinous compositions having improved curingand color clarity properties. Further, of such quaternary ammonium saltsit is believed that the most desirable of such salts for use in theformulation of the additive of the present invention aredicocodimethylammonium chloride, benzyltrimethylammonium chloride,trimethyldodecylammonium chloride dimethylalkyl (C₁₂ -C₁₆)benzylammonium chloride and dimethylstearylbenzylammonium chloride.

The amount of the quaternary ammonium salt employed to catalyze thepolymerization syrup can vary widely and will be dependent to a largedegree upon the acrylic monomer employed in the formulation of thepolymerization syrup, as well as the quaternary ammonium salt chosen asthe catalyst. However, generally the amount of the quaternary ammoniumsalt employed to catalyze the polymerization syrup will be an amountsufficient to provide from about 0.1 to about 15 parts by volume of thecatalyst, based on the total volume of the monomer present in thepolymerization syrup.

PREPARATION OF POLYMERIZATION SYRUP

In the preparation of the polymerization syrup of the present inventionan acrylic monomer satisfying the formula heretofore described isselected. While any suitable acrylic monomer satisfying the definitionof the acrylic monomer set forth hereinbefore can be employed,especially desirable results have been obtained wherein the acrylicmonomer is methyl methacrylate.

The acrylic monomer is transferred to a mixing vessel and effectiveminor amounts of a non-peroxide oxygen donator, such as2,2-bis(allyloxymethyl)-butan-1-ol, a mercaptan and a crosslinking agentcompatible with the acrylic monomer are admixed with the acrylic monomerto form an intimate blend containing from about 300 to 1000 parts byvolume of the acrylic monomer, from about 0.1 to about 1 parts by volumeof the 2,2-bis(allyloxymethyl)-butan-1 ol, from about 0.5 to about 5parts by volume of the mercaptan, and from about 0.3 to about 40 partsby volume of the crosslinking agent.

When the intimate blend of the four described ingredients has beenformulated, the blend is heated to a temperature of from about 80degrees Centigrade to about 110 degrees Centigrade for a period of timeeffective to provide the blend with a desired viscosity. That is, theintimate blend is heated at the specified temperature for a period oftime so that the viscosity of the syrup can be controlled depending uponthe end use for which the polymerization syrup is to be employed.

When the syrup has achieved the desired viscosity, heat is removed andthe blend allowed to cool prior to storage. It should be noted that inthe preparation of the polymerization syrup as set forth above animproved shelf life of the syrup can be achieved, without the need ofrefrigeration or other cooling of the syrup to prevent polymerization ordeterioration of the syrup when same is stored.

While the polymerization syrup prepared in accordance with theprocedures above has exhibited improved shelf life, that is, the syruphas demonstrated a storability of at least six weeks at ambienttemperatures without any detectable changes as to its viscosity ordeterioration, the shelf life of the polymerization syrup can be furtherenhanced by incorporating into the intimate blend, prior to heating,from about 1 to about 100 parts by volume of a polycarbonate compoundcompatible with the acrylic monomer. While any polycarbonate compoundcompatible with the acrylic monomer can be employed, desirable results,have been obtained when the polycarbonate compound is allyl diglycolcarbonate.

To enhance the removal of articles from a mold (when such articles arefabricated of a polymeric resin consisting essentially of thepolymerization syrup as heretofore described and a catalytic amount of aquaternary ammonium salt), an effective minor amount of the internalmold release agent can be incorporated into the intimate blend.

As previously stated, the effective minor amount of the internal moldrelease agent employed can vary widely but will generally be from about0.1 to about 2 parts by volume of the release agent per total volume ofthe syrup. Further, the internal release agent can be any suitablesurfactant which is compatible with the acrylic monomer.

In addition to the internal mold release agent, other additives which donot interfere with the quality or characteristics of the polymerizationsyrup can be incorporated into the syrup. Typical of such otheradditives are coloring agents, ultraviolet absorbers, glass fibers orany other appropriate additive which may be desired dependent on the enduse of the polymerization syrup.

As mentioned above, the polymerization syrup of the present inventionhas a remarkably improved shelf life, and the syrup does not need to bestored in refrigerated conditions to maintain the integrity of thesyrup. In addition, the acrylic resin compositions formulated of thepolymerization syrup and a catalytic amount of a quaternary ammoniumsalt exhibit improved thermal stability without deterioration of theexcellent weathering resistance, transparency and color of the resincomposition.

The unique characteristics of the acrylic resin permit one to cast theresin in four inches or greater thickness, while at the same timeproviding a resin composition which can be cured at ambient temperaturesand atmospheric pressure, and which does not require any post curingtreatment. That is, the unique acrylic resin composition of the presentinvention allows one to substantially reduce the pour to pull time anddoes not require heat or vacuum in order to cure the resin. Under normalcircumstances when employing the acrylic resin of the present invention,the pour to pull time of articles, even those having a thickness of upto about four inches, is less than about 8 hours.

Should one desire to shorten the pour to pull time of the acrylic resinsof the present invention, such can readily be achieved by initiallyheating the mold for a relatively short period of time. While thetemperature to which the mold is heated to enhance curing of the acrylicresin (as well as the period of time the mold is heated) can vary,generally one can enhance the curing of the acrylic resin by heating themold at a temperature of from about 40 degrees Centigrade to 65 degreesCentigrade for a period of up to about 30 minutes without altering theproperties of the acrylic resin.

In order to further illustrate the present invention the followingexamples are given. However, it is to be understood that the examplesare for illustrative purposes only and are not to be construed aslimiting the scope of the subject invention.

EXAMPLE I

Polymerization syrup was prepared by admixing the following ingredientsto form an intimate blend:

500 ml of methyl methacrylate monomer

90 ml of 2,2-bis(allyloxymethyl)-butan-1-ol

1.5 ml of n-octyl mercaptan

40 ml ethylene glycol dimethacrylate

The ingredients were stirred under suitable conditions to insure thatthe intimate blend was obtained and that the blend was substantiallyhomogeneous in nature.

The intimate blend produced above was then heated in a water bathmaintained at approximately 100 degrees Centigrade for a period of from2 to 4 hours. The heating period was varied so as to provide thepolymerization syrup with a predetermined viscosity. When the desiredviscosity had been achieved (such viscosity depending solely upon theend use for the acrylic resin to be formulated from the polymerizationsyrup) the polymerization syrup was allowed to cool, placed in a glasscontainer, and the container was sealed.

The sealed glass container was stored at ambient temperature andatmospheric pressure to determine the shelf life of the polymerizationsyrup. An examination of the syrup was conducted to determine theintegrity of the syrup during the storage period. At the end of a threemonth period a slight deterioration of the syrup was detected, thusillustrating that the syrup containing the methyl methacrylate monomer,2,2-bis(allyloxymethyl)-butan-1-ol, n-octyl mercaptan and ethyleneglycol dimethacrylate had a useful shelf life at ambient temperaturesand atmospheric pressure of about three months.

EXAMPLE II

Polymerization syrup was formulated in accordance with the procedure ofExample I with the exception that 30 ml of a polycarbonate compound (i.eallyl diglycol carbonate) was incorporated into the blend prior toheating. The polymerization syrup containing the polycarbonate compoundwas cooled, placed in a glass container, sealed and stored at ambienttemperature and atmospheric pressure. Examinations of the syrup wereconducted to determine the integrity of the syrup during the storageperiod. It was observed after a nine month storage period that nodeterioration of the syrup could be detected, that is, the viscosity ofthe syrup was substantially unchanged, and no polymerization of themonomer could be detected. Thus, the experiments substantiated that byincorporating a minor effective amount of a polycarbonate compound intothe polymerization syrup of the present invention that a syrup isprovided which has an unexpected, substantially improved shelf life, andthat the syrup can be stored at ambient temperature and atmosphericpressure. That is, the new and unique polymerization syrups of thepresent invention have an improved shelf life and do not requirerefrigeration in order to maintain the integrity of the polymerizationsyrup.

EXAMPLE III

1 ml of benzyltrimethylammonium chloride (a quaternary ammonium saltcatalyst) was admixed with 1000 ml of the syrup prepared using theprocedure of Example I. The resulting resin was poured into molds ofvarious configurations and having thicknesses of from about 1 inch toabout 3 inches. The resin was then allowed to cure at ambienttemperature and atmospheric pressure. The curing time for the resinvaried depending upon the thickness of mold cavity, that is, a moldemployed to fabricate a slab of material having a thickness of about 1inch cured in about 2 hours; whereas the mold employed to fabricate thearticle having a thickness of about 3 inches cured in about 8 hours. Atthe end of the curing period the resulting molded articles were removedfrom the mold. The articles had a tendency to adhere to the surfaces ofthe mold, thus requiring more effort to remove the articles from themold.

EXAMPLE IV

A polymeric resin was formulated utilizing the procedure of Example IIIexcept the syrup was formulated using the procedure of Example II andthe syrup contained about 1.5 parts by volume of sodium dioctylsulfosuccinate, and an anionic surfactant which functioned as aninternal mold release agent. The same molding conditions were carriedout as Example III, and after curing the articles were readily removablefrom the mold without any adherence to the surface of the mold.

EXAMPLE V

A polymeric resin was formulated utilizing the procedure of Example IIIexcept the syrup was formulated using the procedure of Example I and thesyrup contained about 1.5 parts by volume of sodium dioctylsulfosuccinate, and an anionic surfactant which functioned as aninternal mold release agent. The same molding conditions were carriedout as Example III, and after curing the articles were readily removablefrom the mold without any adherence to the surface of the mold.

The articles molded employing the catalyzed polymerization syrups andprocedures set forth above exhibited excellent clarity and improvedresistance to solvent and heat. Further, the articles were extremelydurable and had an improved impact strength when compared to articlesfabricated using conventional acrylic resins.

It is clear that the present invention is well adapted to carry out theobjects and attain the ends and advantages mentioned therein. Whilepresently preferred embodiments of the invention have been described forpurposes of this disclosure, numerous changes may be made which willreadily suggest themselves to those skilled in the art and which areencompassed within the spirit of the invention disclosed and as definedin the appended claims.

What is claimed is:
 1. A polymerization syrup having a improved shelflife, the polymerization syrup consisting essentially of:from about 300to about 1000 parts by volume of an acrylic monomer represented by theformula ##STR5## wherein R is an alkyl moiety containing 1 to about 18carbon atoms; from about 0.1 to about 1 parts by volume2,2-bis(allyloxymethyl)-butan-1-ol; from about 0.5 to about 5 parts byvolume of a mercaptan; and from about 0.3 to about 40 parts by volume ofa crosslinking agent compatible with the acrylic monomer.
 2. Thepolymerization syrup of claim 1 wherein the syrup further includes fromabout 1 to about 100 parts by volume of a polycarbonate compoundcompatible with the acrylic monomer.
 3. The polymerization syrup ofclaim 2 wherein the polycarbonate compound resin is allyl diglycolcarbonate.
 4. The polymerization syrup of claim 1 wherein the mercaptanis represented by the formula

    RSH

wherein R is an alkyl moiety containing from 1 to about 22 carbon atoms.5. The polymerization syrup of claim 4 wherein the acrylic monomer ismethyl methacrylate.
 6. The polymerization syrup of claim 5 wherein themercaptan is n-octyl mercaptan and the crosslinking agent is ethyleneglycol dimethacrylate.
 7. The polymerization syrup of claim 1 whichfurther includes a minor effective amount of an internal mold releaseagent compatible with the acrylic monomer.
 8. The polymerization syrupof claim 7 wherein the minor effective amount of the internal moldrelease agent is an amount sufficient to provide from about 0.01 toabout 2 parts by volume of the internal mold release agent in thepolymerization syrup.
 9. The polymerization syrup of claim 8 wherein theinternal mold release agent is selected from the group consisting ofanionic and nonionic surfactants.
 10. An acrylic resin curable atambient temperature and pressure which comprises an intimate blend of apolymerization syrup and a catalytic amount of a polymerization catalystcapable of effecting polymerization of the syrup, the polymerizationsyrup consisting essentially of:from about 300 to about 1000 parts byvolume of an acrylic monomer represented by the formula ##STR6## whereinR is an alkyl moiety containing 1 to about 8 carbon atoms; from about0.1 to about 1 parts by volume 2,2-bis(allyloxymethyl)-butan-1-ol; fromabout 0.5 to about 5 parts by volume of a mercaptan; and from about 0.3to about 40 parts by volume of a crosslinking agent compatible with theacrylic monomer.
 11. The acrylic resin of claim 10 wherein thepolymerization syrup further includes from about 1 to about 100 parts byvolume of a polycarbonate compound compatible with the acrylic monomer.12. The acrylic resin of claim 11 wherein the polycarbonate compound isallyl diglycol carbonate.
 13. The acrylic resin of claim 11 wherein thepolymerization syrup further includes a minor effective amount of aninternal mold release agent compatible with the acrylic monomer.
 14. Theacrylic resin of claim 13 wherein the minor effective amount of theinternal mold release agent is an amount of from about 0.01 to about 2parts per volume, based on the volume of the syrup.
 15. The acrylicresin of claim 10 wherein the polymerization syrup further includes aminor effective amount of an internal mold release agent compatible withthe acrylic monomer.
 16. The acrylic resin of claim 15 wherein the minoreffective amount of the internal mold release agent is an amount of fromabout 0.01 to about 2 parts per volume, based on the volume of thesyrup.
 17. The acrylic resin of claim 10 wherein the catalytic amount ofthe catalyst for effecting polymerization of the polymerization syrup isfrom about 0.1 to about 15 parts by volume, based on the volume ofmonomer present in the polymerization syrup.
 18. The acrylic resin ofclaim 17 wherein the polymerization catalyst is a quaternary ammoniumsalt.
 19. The acrylic resin of claim 18 wherein the quaternary ammoniumsalt is selected from the group consisting of dicocodimethylammoniumchloride, benzyltrimethylammonium chloride, trimethyldodecylammoniumchloride, dimethylalkyl (C₁₂ -C₁₆) benzylammonium chloride anddimethylstearylbenzylammonium chloride.
 20. The acrylic resin of claim17 wherein the mercaptan is represented by the formula

    RSH

wherein R is an alkyl moiety containing 1 to about 22 carbon atoms. 21.The acrylic resin of claim 20 wherein the acrylic monomer is methylmethacrylate.
 22. The acrylic resin of claim 21 wherein the mercaptan isn-octyl mercaptan and the crosslinking agent is ethylene glycoldimethacrylate.
 23. The acrylic resin of claim 22 wherein thepolymerization syrup further includes from about 0.01 to about 2 partsby volume of an internal mold release agent selected from the groupconsisting of an anionic surfactant and a nonionic surfactant.
 24. Theacrylic resin of claim 23 wherein the internal mold release agent issodium dioctyl sulfosuccinate.